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  1. #1
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    Reach between a 57cm Corsa Extra and 56cm

    A bit of a difficult one to answer...... (please forgive if sounds like a silly one)

    If I were to set up two Corsa Slx's (both regular century geometry).

    One is a 57cm. The other is a 56cm frame.

    Seat height on both is set to 76.5cm (centre BB to top of saddle.)

    Saddle set back (distance measured vertically from nose of saddle to point behind centre of BB) I guess would be different so that a KOPS is acheived.

    Bar height (from floor to top of bar) is set the same on both (only possible I guess if on the 57cm the stem is a distance below the min insertion point)....

    How much difference would the reach be? Am I correct that it could be more than 1cm difference?
    Good bicycles turn effort into emotion.
    They provide the means to reach, and sometimes exceed, your potential.
    On a fine bike you can ride better than you ever thought possible and catch glimpses of extraordinary athletic prowess you didn’t realize you had.
    The experience is inspirational and addictive.
    You long to sustain it.

    ~ jim langley

  2. #2
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    Yes, if the effective top tube difference is more than 1 cm. Measure from the center of the seatpost to the center of the steerer tube on a level plane with the bike on a level floor. That is the best way to measure how the different frame geometries effect the overall reach.
    “It is just a ‘Game Boy’ that has a gigolo attached at the end telling the racer when to take a piss,” Hinault

  3. #3
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    From the merckx century geometry charts on this board I realize that a 57cm frame has a 56.8cm TT and the 56cm frame has a 56cm TT.

    But, I am aware that Seat and Head tube angles will affect that reach / top tube measurement (57cm has ST angle of 72.39º and the 56cm has ST angle of 72.52º).

    FWIW I currently ride 57cm merckx steel frames and wondered if the bursa's on my hip joints might be caused by the fact that I am approx 4-5cm or more in front of a kops fit (even with the Thomson in line seat pin). I use a foam roller to release my IT bands and this helps somewhat but I'm considering moving to a 56cm frame so I can get further behind the BB as I think this could make a difference (FYI I don't have the same fit problem with the alu/carbon Condor frame I ride as it has a effective TT of 55cm) But Im not so sure of going down to a 55cm merckx as the head tube will be too short (130mm tall)

    Being cursed with long legs in comparison to torso (over 34.5" inseam and just short of 6' tall) I already ride the 57cm Corsa SL with a 95mm stem so am not keen to use a stem shorter than this - Ive got an 85mm cinelli but I don't believe another 10mm would make much difference.

    Sorry if this seems a bit irrelevant to the original post. Im just trying to work out how much shorter I could make the cockpit of a 56cm frame fit without going too short on the stem length.
    Good bicycles turn effort into emotion.
    They provide the means to reach, and sometimes exceed, your potential.
    On a fine bike you can ride better than you ever thought possible and catch glimpses of extraordinary athletic prowess you didn’t realize you had.
    The experience is inspirational and addictive.
    You long to sustain it.

    ~ jim langley

  4. #4
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    The effective difference in top tube length would be less than 1 cm, probably closer to 0.5 cm because the 56 has a steeper STA. Are you sure the 56 would be large enough for you? My saddle height is 75 cm, and I ride a 57 Merckx and could probably handle a 58.

    Have you tried putting a shorter stem on your 57 and moving your saddle back?

  5. #5
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    Long time ago I downloaded an amazing excel file comparing two bike geometries- credits and thanks to "Clary" . The original source is gone by now. I only found early version here .
    PM me, I can send you the much improved version 1.7 (which includes also seat position).
    (even with my 56 Strada data already in )

  6. #6
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    Quote Originally Posted by tarwheel2
    The effective difference in top tube length would be less than 1 cm, probably closer to 0.5 cm because the 56 has a steeper STA. Are you sure the 56 would be large enough for you? My saddle height is 75 cm, and I ride a 57 Merckx and could probably handle a 58.

    Have you tried putting a shorter stem on your 57 and moving your saddle back?
    Hi Tarwheel,

    I'd hoped you might be able to help answer this one as I saw an old post of your's discussing ST / HT angles affecting overall cockpit reach.

    FWIW I ride with a saddle height of 76.5cm and 95mm stem on my 57cm merckx frames.

    I know it sounds daft but I'd never taken a proper Kops measurement (ie with the help of a friend) so measurements I'd taken myself, I now realize, were incorrect.

    After some more measurements recently, I've found that I'm quite a way off. After moving the saddle back to a better position I'm now too far from the hoods, my torso doesn't feel upright enough, and I feel more comfortable on the cross bar (fyi to compliment my riding I do regular strength work and yoga .... I can hear the laughs already! so Im pretty sure it's not a flexibility issue). Incidentally my first Corsa Extra was a 58cm that was too long.
    Good bicycles turn effort into emotion.
    They provide the means to reach, and sometimes exceed, your potential.
    On a fine bike you can ride better than you ever thought possible and catch glimpses of extraordinary athletic prowess you didn’t realize you had.
    The experience is inspirational and addictive.
    You long to sustain it.

    ~ jim langley

  7. #7
    Eddy 53:11
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    I don't mean to hi-jack here, but I was just about to post a similar thread.

    I have a 1989 TSX I have measured (c-c on top tube) several times to be a 55cm.
    I'm pretty much a 54cm rider with a 100mm stem.

    What I can't figure out is that the 55cm with a 120 quill seems to fit really nearly perfectly! (??)
    Is older Merckx sizing closer to a 1/2 cm/size DOWN? Meaning a 55 is really a 54(ish)?

    I dont' know if a 54cm in the same mode/yearl would be too smal(ish)l for me? Am I alone here?
    Live vicariously through yourself.

  8. #8
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    Quote Originally Posted by JetSpeed
    I don't mean to hi-jack here, but I was just about to post a similar thread.

    I have a 1989 TSX I have measured (c-c on top tube) several times to be a 55cm.
    I'm pretty much a 54cm rider with a 100mm stem.

    What I can't figure out is that the 55cm with a 120 quill seems to fit really nearly perfectly! (??)
    Is older Merckx sizing closer to a 1/2 cm/size DOWN? Meaning a 55 is really a 54(ish)?

    I dont' know if a 54cm in the same mode/yearl would be too smal(ish)l for me? Am I alone here?
    Not all Merckx have the same seat tube angles, so that could affect the fit. Generally speaking, a frame with a more relaxed STA (eg, 72.5) will fit shorter than the same size top tube with a steeper angle (eg, 74) -- assuming you keep your saddle positioned the same with regards to the BB or pedals.

    Within the same frame models, STA angles are generally more relaxed in larger sizes. For example, a size 54 might have a 74 STA and the same frame in size 57 might have a 72.5 STA. Also, different Merckx models have different geometries. The classic Merckx Century geometry frames have relatively relaxed STAs, such as 72.5 in size 57. However, Merckx also made some frames with their "crit" geometry that have steeper STAs -- such as 74 in a size 57 frame.

  9. #9
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    Quote Originally Posted by bolo yeung
    Hi Tarwheel,

    I'd hoped you might be able to help answer this one as I saw an old post of your's discussing ST / HT angles affecting overall cockpit reach.

    FWIW I ride with a saddle height of 76.5cm and 95mm stem on my 57cm merckx frames.

    I know it sounds daft but I'd never taken a proper Kops measurement (ie with the help of a friend) so measurements I'd taken myself, I now realize, were incorrect.

    After some more measurements recently, I've found that I'm quite a way off. After moving the saddle back to a better position I'm now too far from the hoods, my torso doesn't feel upright enough, and I feel more comfortable on the cross bar (fyi to compliment my riding I do regular strength work and yoga .... I can hear the laughs already! so Im pretty sure it's not a flexibility issue). Incidentally my first Corsa Extra was a 58cm that was too long.
    KOPs is more a general guideline or starting point rather than a hard-and-fast rule. If you were comfortable with your original saddle position, you might want to just go back to it. Also, raising your handlebars will shorten the reach, if that is a viable option for you.

    BTW, I've got two Merckx frames (Corsa 01 and AX) in the same size and thought I had them set up identically. However, I measured the saddle to handlebar distance one day last fall because the AX was feeling a little too spread out and realized that the saddle was about 1.5 cm further back. I think it had gradually moved back over time due to the seatpost clamp not being tight enough. Anyway, I moved it forward so the reach would be the same on both bikes and it felt just right. It wasn't bothering my knees or noticeably affecting my performance in either position.

    Saddle height, in my experience, can have very noticeable effects on performance and proper fit. I have had saddle posts slip any number of times when the clamp wasn't tight enough, and I generally notice it during the ride because climbing becomes more difficult. I've also hurt my knees when this has happened, so I pay close attention to saddle height. Just last weekend, I noticed that my reach seemed to be getting longer during a ride because the front hub was no longer blocked in my vision by the handlebar. I had changed seat posts before the ride, so was paying attention. At first I thought the saddle had slid backwards, but the reach was the same when I measured it. However, the seat post had slipped down about 1 cm in the clamp when I measured it. I have a history of breaking seat post bolts, so had not tightened down hard enough for fear of breaking another one.
    Last edited by tarwheel2; 03-25-2011 at 08:19 AM.

  10. #10
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    I realise now you were correct that a 56cm would have been too small.

    After spending some time with a friend from the club on a turbo trainer and on the road we've made some adjustments that have made a noticeable improvement to how my IT bands have been feeling (as well as using a foam roller almost every evening to alleviate any inflammation of the bursae).

    With regards to shortening the cockpit we've moved the ergo's up the bars a very small amount (maybe hald of an inch?) and this alone made a world of difference. Like other riders on here I favour the rivendell/noodle bars and I had the ergos set up so the hoods were parallel with the floor (in the same way that they advertise the Nitto Noodles on the Rivendell site). With a 90mm XA stem it's worked out very well.

    Anyway to add to this, the 57cm NOS MXL I've been piecing together has an uncut fork steerer which means I can have the bars just that little higher. I've included some pics as I'm extremely pleased with the build.

    http://i1109.photobucket.com/albums/...OS_mxl_012.jpg

    http://i1109.photobucket.com/albums/...OS_mxl_022.jpg

    http://i1109.photobucket.com/albums/...OS_mxl_018.jpg
    Good bicycles turn effort into emotion.
    They provide the means to reach, and sometimes exceed, your potential.
    On a fine bike you can ride better than you ever thought possible and catch glimpses of extraordinary athletic prowess you didn’t realize you had.
    The experience is inspirational and addictive.
    You long to sustain it.

    ~ jim langley

  11. #11
    em3
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    Jim, if you are seeking a shorter reach (to the hoods) you need to get some different bars. The Nitto Noodles you are riding have the most extreme reach/drop available on a road bar (95mm/140mm).Try a Deda shallow, which has similar classic bend, but a 80mm/135mm reach/drop.
    EM3

  12. #12
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    Thanks.
    Good bicycles turn effort into emotion.
    They provide the means to reach, and sometimes exceed, your potential.
    On a fine bike you can ride better than you ever thought possible and catch glimpses of extraordinary athletic prowess you didn’t realize you had.
    The experience is inspirational and addictive.
    You long to sustain it.

    ~ jim langley

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